1. Field
Embodiments of the disclosure relate generally to the field of propellant mass remaining calculation for propellant (such as xenon) tanks and more particularly to a method for calculating mass of xenon as a non-ideal gas using controlled temperature differential to induce associated pressure differential allowing an iterative differential pressure and temperature calculation with known tank volume to back calculate xenon mass remaining.
2. Background
Xenon thrusters are employed in many spacecraft applications for station keeping and on-orbit maneuvering. Xenon used as a propellant is a non-ideal gas. Propellant quantity gauging for xenon in microgravity is therefore very difficult along the pressure-temperature-density inflection zone because small changes in pressure or temperature can change the calculated density by over 100%. Diurnal effects impact gauging measurements due to changing environmental conditions of the spacecraft. Additionally, small biases or inaccuracies in the telemetry can also cause significant uncertainty in mass remaining. Current quantity gauging is accomplished by book-keeping methods subtracting estimated amounts of propellant processed during each thruster operation for defining remaining quantity of propellant until quantity and associated pressure in the tank drops below approximately 1 MPa at which point ideal gas calculations for mass based on pressure, volume, density, and temperature can be assumed with reasonable accuracy.
It is therefore desirable to provide a method for calculation of xenon mass in a propellant tank which corrects for non-ideal gas properties and sensor biases for a range of propellant quantities in which ideal gas calculations cannot be accurately used.